Perhaps it has been mentioned here before....but I just noticed it. In the "Chicken Roaster" episode, Kramer pretends to mug George and is later recognized by a German woman (from the tourist bus) yelling "Stop that man!" in the street. Identical to the scene in Marathon Man where a woman in New York's diamond district recognizes the Nazi dentist played by Laurence Olivier.
I certainly have seen this episode a few times before, but just noticed this now - a testament to the continued wealth of discovery in the Seinfeld canon.